Data Format
3.3Defect Management
3.3.1Defect list
Information of the defect location on the disk is managed by the defect list. The following are defect lists which the HDDs manage.
•P list (Primary defect list): This list consists of defect location information available at the disk drive shipment and is recorded in a system space. The defects in this list are permanent, so the INIT must execute the alternate block allocation using this list when initializing the disk.
•D list (Data defect list): This list consists of defect location information specified in a FORMAT UNIT command by the INIT at the initialization of the disk. This information is recorded in the system space of the disk drive as the G list. To execute the alternate block allocation, the FORMAT UNIT command must be specified.
•G list (Growth defect list): This list consists of defective logical data block location information specified in a REASSIGN BLOCKS command by the INIT, information on defective logical data blocks assigned alternate blocks by means of the HDD automatic alternate block allocation, information specified as the D list, and information generated as the C list. They are recorded in the system space on the disk drive.
The INIT can read out the contents of the P and G lists by the READ DEFECT DATA command.
3.3.2Alternate block allocation
The alternate data block is allocated to a defective data block (= sectors) in defective sector units by means of the defect management method inside the HDDs.
The INIT can access all logical data blocks in the user space, as long as there is no error.
Spare sectors to which alternate blocks are allocated can be provided in "alternate cylinders". See Subsection 3.1.2 for details.
The INIT can specify the size and area for spare sectors by the MODE SELECT command at the time of the initialization of the disk.
Both of the following are applicable to the alternate block allocation.
•Sector slip treatment: Defective sectors are skipped and the logical data block corresponding to those sectors is allocated to the next physical sectors. This treatment is made on the same cell as the defective sector's and is effective until all spare sectors in that cell are used up.
•Alternate sector treatment: The logical data block corresponding to defective sectors is allocated to unused spare sectors in the alternate cylinder.
The alternate block allocation is executed by the FORMAT UNIT command, the REASSIGN BLOCKS command, or the automatic alternate block allocation. Refer to Chapter 4 “Command Specifications” and Subsection 5.3.2 “Auto alternate block allocation processing” of the Interface Specifications for details of specifications on these commands. The logical data block is allocated to the next physically continued sectors after the above sector slip treatment is made. On the other hand, the logical data block is allocated to spare sectors which are not physically consecutive to the adjacent logical data blocks. If a command which processes several logical data blocks is specified, the HDDs process those blocks in ascending order of logical data block.